1. Field of the Invention
This invention relates to magnetic proximity sensing devices, and more specifically, to a design for a pivoting armature and its cooperation with different polarities of permanent magnets for enhancing the sensitivity of the device.
2. Description of the Prior Art
In general, magnetically actuated proximity switches are used to sense relative movement between two members; one being the switch itself, and the other being a magnetically permeable member of either iron or steel.
U.S. Pat. No. 4,225,837 discloses a pivotal armature which carries the contacts and which is provided at its ends with magnetically permeable lips extending toward the marginal area of the same magnetic sign pole faces of permanent magnets with which the armature cooperates. In order to create a greater pull or to maintain the pivotal armature in a horizontal disposition, a lesser air gap between the magnet and the armature exists on the one side of the device with a greater air gap on the other side. This magnet spacing between the lips requires that both magnets be identical in strength in their magnetic pull so as to eliminate the possibility of the magnetic influence from varying during operation of the switch. The pole faces of the magnets influencing the lips of the contact bridge is of the same polarity sign. The providing of identical polarity magnets requires labor intensive testing and manual positioning and respositioning of the magnets in order to attain the required magnetically flux intensity. Also, the method for decreasing the strength of one pole of the same magnet to create flux differential requires sophisticated equipment and test facilities to insure that the correct amount of imbalance for pivotal movement of an armature is consistently achieved in the operation of the device.
Other examples of magnetically operating proximity sensing devices are disclosed in U.S. Pat. Nos. 3,176,096; 3,325,756; 3,361,995; 3,673,527; 3,732,512; and 4,117,431.
There is lacking in the prior art, particularly in the switch design of the former U.S. Pat. No. 4,225,837, the ability to consistently obtain an adequate contact pressure between the electrical contacts of the switch at reasonable sensing distances. There is further lacking such a device capable of providing ample current carrying capabilities of the contact member. There is further lacking in the prior art disclosures the teaching of non-spacing of the magnets or non-weakening of the magnetic fields which conventionally provides magnetic imbalance to allow the pivoting or movement of the armature.
There is further lacking in the prior art a design for an armature which eliminates the need for mounting a pair of contacts whose cooperation with another pair of contacts operates the device. There is further lacking in the prior art an armature having means extending towards its opposed ends having different lengths and masses cooperating with different pole faces of an associated permanent magnet. There is further lacking in the piror art means extending from the opposed ends of a pivotal armature employed as both a contact surface and a means for enhancing sensitivity. There is further lacking in the prior art a proximity switch which does not require labor intensive testing and manual positioning of the magnets for its optimum operation.